fix(hysteria2): default the port to 443 when the share URI omits it (#10026)

The Hysteria2 URI scheme makes the port optional: "The hostname and
optional port of the server. If the port is omitted, it defaults to 443."
`Hysteria2Fmt.Resolve` assigned `url.Port` straight through, and
`System.Uri` answers -1 for an unregistered scheme that carries no port,
so `hysteria2://password@hy2.example/` imported as a profile with
`Port = -1`. `ProfileItem.IsValid` rejects any port outside 1..65535, so
such a link produced a profile that could never be used, and nothing said
why.

-1 is the only value that means "the port was omitted"; a ':' with no
digits after it maps to -1 as well. An explicit ":0" parses as 0 and
keeps the fate it has today - rejected by `IsValid` - rather than being
redirected to a server the link never named.

`ResolveRealm` takes its port from `HyRealm.RendezvousPort` instead of
the URI, so it is unaffected.

The added tests cover both spellings of the scheme, with and without a
trailing slash, a bare ':', and the resulting profile's validity. Two of
them are controls: an explicit port is still preserved, and an explicit
":0" still does not turn into 443.

v2rayN/ServiceLib/Handler/Fmt/Hysteria2Fmt.cs

@@ -17,7 +17,11 @@ public class Hysteria2Fmt : BaseFmt
         }
 
         item.Address = url.IdnHost;
-        item.Port = url.Port;
+        // The URI scheme makes the port optional and defaults it to 443. Uri.Port answers -1 for
+        // an unregistered scheme carrying no port, which ProfileItem.IsValid then rejects.
+        // Only -1 means "omitted": an explicit ":0" has to stay 0 and be rejected the way it
+        // always was, instead of being quietly redirected to a server the link never named.
+        item.Port = url.Port == -1 ? 443 : url.Port;
         item.Remarks = url.GetComponents(UriComponents.Fragment, UriFormat.Unescaped);
         item.Password = Utils.UrlDecode(url.UserInfo);